The present invention relates to scene analysis apparatus and methods and more particularly, to a method and apparatus for analyzing a scene at two different resolutions.
In many areas of particle analysis, such as, blood cell analysis or pap smear analysis, the particles of interest are widely distributed in a field and are surrounded by many particles of no interest at all. For example, white blood cells may be surrounded by hundreds of red blood cells while cancerous or dysplastic cervical cells may be surrounded by tens-to-thousands of normal cervical cells and debris.
It is desirable to analyze in detail only the particles of interest in the scene. This can be accomplished by the detailed analysis of all objects in order to exclude the unwanted objects. However, this technique is very time-consuming and therefore relatively impractical from a commercial standpoint. Alternately, one can use a single sensor to perform a preliminary analysis of all particles at a low resolution and then switch the sensor to a higher resolution for further analysis when a particle of interest is found in the sample. However, this method requires mechanical or electrical switching of the analysis resolution with a concomitant limitation of a single mode of analysis at any given time.
The use of simultaneous multiple resolution analysis of a plurality of fields overcomes the limitations of prior art analysis systems. Dual resolution scanning systems have been used by several workers. Aldrich et al disclose in U.S. Pat. No. 3,448,271 a dual resolution scanning system which centers and tracks celestial objects. In this system two coaxial images at different magnifications are employed to acquire and track stars or the solar disc. The scanned output of a single sensor is used as an on or off-axis signal in a feedback loop to center the star image on the optical axis. No image analysis of the celestial objects is performed or envisioned. In fact, the superimposed images on the single detector would confuse an attempt to analyze the scanner output.
Simularly, Ward in U.S. Pat. No. 3,614,449 discloses a dual resolution scanning system for acquiring and tracking a distant source of light (the target). Ward describes the same type coaxial dual resolution system in which both images are projected onto a single sensor. In addition, there is a second sensor responsive to a narrow spectral band ranging source emitted by the systen and reflected by the target. Although the ranging subsystem is functionally separate from the dual resolution centering and tracking system, it is housed in the same assembly for compactness in a NASA application. Again, there is no inmage analysis disclosed or envisioned by either the acquiring-tracking system or the ranging subsystem.
Other uses of dual resolution scanning have been disclosed, such as Gard in U.S. Pat. No. 3,804,976, which uses the scanned images for display purposes. However, no image analysis is revealed or envisioned by these disclosures.
Adkins in U.S. Pat. No. 3,864,564 discloses a dual resolution scanning system in which a low resolution, one dimensional scan is used for finding and positioning a blood cell, and a high resolution two-dimensional scan is used to analyze the cell. The high resolution sensor is a videcon type T.V. camera which is well suited to the analysis of the centered blood cell. However, the low resolution sensor is a single photodetector. The image is swept across the photodetector by means of a rotating mirror thereby producing a one-dimensional line scan of the low resolution scene. The low resolution signal is used only to detect and center the cell for analysis by the high resolution sensor. Analysis by the low resolution portion of the system is not disclosed or envisioned. In fact, any analysis using the onedimensional information provided by the low resolution line scanner would be difficult and limited.
A system such as that described by Adkins has several limitations. To use the blood cell example, if there were several classses of cells detected by the low resolution acquisition and centering system, and it was desired to perform a detailed analysis on only a subset of these cells, it would be necessary to acquire and center all detected cells and perform a detailed analysis on them all using Adkins system. Thus much additional unnecessary effort would be necessary. In the case of pap smears, where there may be thousands of normal cells to every cancer cell, the extra work necessary to perform a detailed analysis on every normal cell to find a single cancer cell would render a commercial application impractical.
In many cases it is possible to derive enough information from a preliminary low resolution analysis to determine if a detected object warrants further detailed analysis. The present invention provides for such dual resolution analysis with the low resolution analysis of a large field occurring simultaneously with the high resolution analysis of an object of interest. Using the previously mentioned blood cell example, artifacts such as dirt or large stain crystals can and do occur on blood smears. A simple preliminary measurement of object size is usually adequate to allow exclusion of these artifacts from the detailed high resolution analysis. A more complex low resolution analysis can be employed if desired
It is accordingly, a general object of the invention to provide a method and apparatus for scene analysis which overcomes the limitations of the prior art systems.
It is a specific object of the invention to provide a method and apparatus for dual resolution analysis of a scene.
In the accomplishment of these objects, two sensors are employed: one covering a large field at a low resolution and the other covering a smaller field at a higher resolution. The low resolution field of view (large field) is located in a known relationship to the higher resolution field of view (the small field). Given the known relationship of the resolution fields, the low resolution analysis reveals the presence of an object of interest. The object of interest is moved into the higher resolution field for further detailed analysis while continuing the analysis of the scene or sample at the low resolution to detect any other objects of interest. Thus, a plurality of degrees of resolution analysis can occur substantially simultaneously.